Maybe I'm just reading into what is being asked here. So when you come to a stop, how much is your rear actually lowering? Is it for a few secs or longer. How hard are you braking?
Even though I've been riding a spyder since '09, I just got this RT in July. My wife is trying to "steal" riding time from me, but before she hits the road, we've been practicing in a school parking lot. Since I'm watching from the street, I can hear a lot more of what the bike is doing than when I'm on it. So the manual says it automatically adjusts for road conditions and load changes (weight). So that tells me the there is a predetermine ride height that it wants to maintain.
So during hard braking exercises (unloading the rear end), I can hear a psssst (air being released from the air bag). I haven't really paid attention to see how much the rear was lowering to get to the predetermined ride height. I can't really hear if the compressor is activated when she rides away, but I'm sure it adds a lil air to compensate for the rear "squatting"(loading the rear end) when the throttle is applied.
So I don't think you have a leaking air bag, or you would hear not only when you stop, but it would continue when you shut the bike off. One way to check would be to shutoff the bike when the rear end starts to lower/ hear the air venting out. (In a safe area of course).
Maybe more seasoned RT owners can chime in with better info. Just like you, I'm just learning about the RT, and I would like to know if something is wrong with my spyder.